1. Field of the Invention
The present invention relates to an anchorage for a steel wire strand for prestressed concrete (hereinafter referred to as PC wire strand) suitable for prestressed concrete members or members of a staycable wherein an anchoring means is used in an embedded state.
2. Description of the Prior Art
Heretofore, in a prestressed concrete member wherein an anchoring means is used in an embedded state and not used repeatedly, for example, in post-tensioned concrete member or in a centrifugally processed pretension prestressed concrete pile (hereinafter referred to as PC pile) or the like, there has been used a steel wire or bar as steel material for prestressed concrete (hereinafter referred to as PC steel material), an end portion of which is subjected to heading at a warm (100.degree.-500.degree. C.) or cold region to form an enlarged anchor portion permitting an embedded use of the steel wire or bar. However, the recent tendency to enhancement of strength of the aforementioned pile or the like has given rise to an increasing demand for a PC steel material of larger diameter and of higher strength. In this case, wire for prestressed concrete (hereinafter referred to as PC wire) encounters a limit as to the enlargement of its diameter and enhancement of its strength, and the PC steel bar also encounters a limit as to the enhancement of its strength. On the other hand, PC wire strands can easily be thickened in diameter and strengthened and are superior with respect to economy, so their application to the foregoing pile or the like is now in demand. However, the fact is that as an anchoring means for an end portion of PC wire strands there has not yet been developed a structure which is inexpensive and compact.
More particularly, the PC wire strand usually is anchored by means such as an anchoring member in the form of a chuck or a compression grip, but these anchor fittings are expensive and large-sized. It has also been tried to apply the foregoing heading anchor method to the PC wire strand, but this has not been practically used yet because in this case the resultant enlarged head portion is deficient in strength with a breaking strength that is 40 to 60% of the breaking strength of the PC wire strand.
Further, the PC wire strand is also anchored by means of a combination of forming the end portion of the PC wire strand into an enlarged head and clamping an adjacent portion of said PC wire strand by wedges as shown in U.S. Pat. No. 3,820,832. However, in this kind of anchoring means, the tension or the stress force of the PC wire strand is undertaken by the wedge anchor only and the enlarged head of PC wire strand assists in transmitting said force to the wedges. Therefore, such an anchor fitting is large-sized and expensive for embedded use. Another function of the enlarged head of PC wire strand in this invention is the prevention of undesired slippage of the strand in the wedges and ejection of the wedges from the anchor sleeve by jerky movements.